/*
 * Copyright (C) 2005 Luca Veltri - University of Parma - Italy
 * 
 * This file is part of MjSip (http://www.mjsip.org)
 * 
 * MjSip is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 * 
 * MjSip is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with MjSip; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 * 
 * Author(s):
 * Luca Veltri (luca.veltri@unipr.it)
 */

package org.zoolu.util;



/** Simple and fast hash/message-digest algorithm.
  */
public class SimpleDigest extends MessageDigest {
	

	// ************************* Attributes *************************

	/** The digest */
	byte[] message_digest;

	/** Whether is finalized. */
	boolean is_done;

	/** Index within the message_digest. */
	int index;

	/** Add term */
	byte add_term;

	
	// *********************** Public methods ***********************

	/** Constructor */
	public SimpleDigest(int size) {
		init(size);
	}


	/** Constructor */
	public SimpleDigest(int size, byte[] buffer) {
		init(size);
		update(buffer);
	}


	/** Constructor */
	public SimpleDigest(int size, byte[] buffer, int offset, int len) {
		init(size);
		update(buffer,offset,len);
	}


	/** Constructor */
	public SimpleDigest(int size, String str) {
		init(size);
		update(str);
	}


	/** Inits the SimpleDigest */
	private void init(int size) {
		is_done=false;
		message_digest=new byte[size];
		for (int i=0; i<size; i++) message_digest[i]=(byte)(i);
		index=0;
		add_term=0;
	}


	/** MessageDigest block update operation.
	  * Continues a message-digest operation,
	  * processing another message block, and updating the context. */
	@Override
	public MessageDigest update(byte[] buffer, int offset, int len) {
		
		if (is_done) return this;
		//else
		 
		for (int i=0; i<len; i++) {
			if (index==message_digest.length) index=0;
			add_term+=buffer[offset+i];
			message_digest[index]=(byte)(message_digest[index]^add_term);
			index++;
		}
		return this;
	}


	/** MessageDigest finalization. Ends a message-digest operation, writing the
	  * the message digest and zeroizing the context. */
	@Override
	public byte[] doFinal() {
		
		if (is_done) return message_digest;
		//else

		int k=message_digest.length-index;
		while (index<message_digest.length) {
			message_digest[index]=(byte)(message_digest[index]^(k));
			index++;
			k++;
		}     
		for (int i=0; i<message_digest.length; i++) message_digest[i]=(byte)(message_digest[i]^add_term);    

		return message_digest;
	}

	
	/** Calculates the SimpleDigest. */
	public static byte[] digest(int size, byte[] buffer, int offset, int len) {
		MessageDigest md=new SimpleDigest(size,buffer,offset,len);
		return md.doFinal();
	}


	/** Calculates the SimpleDigest. */
	public static byte[] digest(int size, byte[] buffer) {
		return digest(size,buffer,0,buffer.length);
	}


	/** Calculates the SimpleDigest. */
	public static byte[] digest(int size, String str) {
		MessageDigest md=new SimpleDigest(size,str);
		return md.doFinal();
	}
	
}
